JP2018062701A - Magnesium alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnesium alloy excellent in heat resistance.SOLUTION: A magnesium alloy contains Al as much as 4.5 mass% or more and 5.5 mass% or less, a rare-earth element as much as 1.7 mass% or more and 2.3 mass% or less, Ca as much as 0.7 mass% or more and 1.3 mass% or less, Sr as much as 0.2 mass % or more and 0.5 mass% or less, and Mn as much as 0.2 mass% or more and 0.5 mass% or less, and has a residue comprising Mg and inevitable impurities.SELECTED DRAWING: None

Description

  The present invention relates to a magnesium alloy.

  Magnesium alloys are attracting attention as lightweight materials because they have the lowest specific gravity among practical metals and are excellent in specific strength and specific rigidity. The magnesium alloy has various characteristics by containing various additive elements (for example, Patent Document 1 and Patent Document 2).

JP 2012-136727 A JP 2010-242146 A

  Development of magnesium alloys with excellent heat resistance is desired. Parts such as automobile parts and aircraft parts may have a use environment temperature higher than room temperature. For example, the parts disposed near the engine room may have a use environment temperature of about 100 ° C. to 180 ° C., and are preferably excellent in heat resistance.

  An object of the present disclosure is to provide a magnesium alloy having excellent heat resistance.

The magnesium alloy according to the present disclosure is
Al is 4.5 mass% or more and 5.5 mass% or less,
1.7% to 2.3% by mass of rare earth elements,
Ca is 0.7 mass% or more and 1.3 mass% or less,
Sr is 0.2% by mass or more and 0.5% by mass or less,
Containing 0.2% by mass or more and 0.5% by mass or less of Mn,
Magnesium alloy with the balance being Mg and inevitable impurities.

  The magnesium alloy of the present disclosure is excellent in heat resistance.

Sample No. produced in Test Example 1 It is the microscope picture which observed the section of 1-4 die-casting materials with the scanning electron microscope (SEM). 6 is a graph showing the relationship between the Al content and the residual axial force shown in Test Example 1. 6 is a graph showing the relationship between the rare earth element content and the residual axial force shown in Test Example 2. 6 is a graph showing the relationship between Ca content and residual axial force shown in Test Example 3.

[Description of Embodiment of the Present Invention]
The present inventors diligently studied the kind and content of additive elements in order to produce a magnesium alloy having excellent heat resistance. Usually, the cast member (die-cast material) produced with a magnesium alloy is used in the state fixed to the other member. For fixing, iron-based alloy bolts and the like are often used from the viewpoint of cost. In that case, when the cast member is exposed to a high temperature, the thermal expansion coefficient of the magnesium alloy is larger than the thermal expansion coefficient of the bolt of the iron-based alloy, so that a large compressive stress acts on the magnesium alloy. That is, when an actual use mode is taken into consideration, as heat resistance, resistance to compressive stress in a high temperature environment is important. In view of this point, the present inventors consider how much the fastening force (residual axial force) of the bolt is maintained when the cast member is bolted, exposed to a high temperature environment, and then returned to a normal temperature environment. From the viewpoint, as a result of evaluating the heat resistance of the magnesium alloy, a tendency different from the high temperature creep resistance by the tensile creep test was found. Then, the composition of the magnesium alloy which can improve the heat resistance of the magnesium alloy evaluated by residual axial force was examined. As a result, when aluminum (Al), rare earth element (RE), strontium (Sr), calcium (Ca), and manganese (Mn) are used as additive elements, the addition amount of these additive elements is limited to a relatively narrow range. Furthermore, the inventors have found that the heat resistance (residual axial force) of the magnesium alloy is remarkably improved. The present invention is based on the above findings. First, the contents of the embodiments of the present invention will be listed and described.

(1) A magnesium alloy according to an aspect of the present invention is
Al is 4.5 mass% or more and 5.5 mass% or less,
1.7% to 2.3% by mass of rare earth elements,
Ca is 0.7 mass% or more and 1.3 mass% or less,
Sr is 0.2% by mass or more and 0.5% by mass or less,
Containing 0.2% by mass or more and 0.5% by mass or less of Mn,
Magnesium alloy with the balance being Mg and inevitable impurities.

  A magnesium alloy containing an additive element in the above range is remarkably excellent in heat resistance evaluated by residual axial force. The magnesium alloy can achieve remarkably excellent heat resistance because it contains a specific additive element in the magnesium alloy and the addition amount is limited to a relatively narrow range, as shown in test examples described later. Because it is. Magnesium alloys having excellent heat resistance can be suitably used for materials such as automobile parts and aircraft parts.

(2) As one form of the magnesium alloy,
A form in which the area ratio of the compound containing Mg and Al in the cross section is 5% or less can be given.

  Since the compound containing Mg and Al has a relatively low melting point, if the area ratio of the compound is 5% or less, it is easy to suppress a decrease in heat resistance of the magnesium alloy evaluated by the residual axial force.

(3) As one form of the magnesium alloy,
The form whose content of Al is 4.8 mass% or more and 5.3 mass% or less can be mentioned.

  By restricting the Al content in the magnesium alloy to the above range, the heat resistance of the magnesium alloy of the magnesium alloy evaluated by the residual axial force can be further improved.

[Details of the embodiment of the present invention]
Details of the embodiment of the present invention will be described below.

<Magnesium alloy>
The magnesium alloy according to the embodiment contains specific amounts of Al, rare earth elements, Ca, Sr, and Mn as additive elements, with the balance being Mg and inevitable impurities. Specifically, Al is 4.5 mass% or more and 5.5 mass% or less, Rare earth element is 1.7 mass% or more and 2.3 mass% or less, and Ca is 0.7 mass% or more and 1.3 mass% or less. , Sr is 0.2% by mass or more and 0.5% by mass or less, Mn is 0.2% by mass or more and 0.5% by mass or less, and the balance is Mg and an inevitable impurity magnesium alloy. One of the features of this Mg alloy is that the content of each element is limited to a relatively narrow range as shown in the above composition.

[Aluminum (Al)]
Al not only improves the heat resistance of the magnesium alloy evaluated by the residual axial force, but also improves the high temperature creep resistance by a tensile creep test. Al also improves mechanical properties of Mg alloy such as corrosion resistance, strength, and plastic deformation resistance. Al is present in the alloy structure by forming a compound containing Sr (Al—Sr compound), a compound containing Ca (Al—Ca compound), and the like. Details of each compound will be described later.

  The Al content is 4.5% by mass or more and 5.5% by mass or less. By making the Al content 4.5% by mass or more, the Al—Sr compound and the Al—Ca compound can be easily formed sufficiently, and the heat resistance and high temperature creep resistance of the magnesium alloy evaluated by the residual axial force can be improved. Easy to improve. By setting the Al content to 5.5% by mass or less, the magnesium alloy can have appropriate toughness. Moreover, it can suppress that the compound (Mg-Al compound) containing Mg is excessively formed (precipitation) in a magnesium alloy by making content of Al below 5.5 mass%, It is easy to suppress a decrease in residual axial force and high temperature creep resistance. The content of Al is further preferably 4.8% by mass to 5.3% by mass. If the Al content is 4.8% by mass or more, the melting point of the magnesium alloy is lowered, so that the hot water flowability is improved, so that the castability is easily improved. If the Al content is 5.3% by mass or less, the formation of the Mg—Al compound is easily suppressed, and the heat resistance is further improved.

[Rare earth elements (RE)]
RE improves the heat resistance of the magnesium alloy evaluated by the residual axial force. RE also contributes to the improvement of high-temperature creep resistance against pulling. RE forms a compound containing Al (Al-RE compound) and exists in the alloy structure. The formation of the Al—RE compound suppresses the formation (precipitation) of the Mg—Al compound. RE is at least one rare earth element selected from Group 3 elements of the periodic table, that is, scandium (Sc), yttrium (Y), lanthanoid, and actinoid, and is an alloy containing a plurality of rare earth elements. Including misch metal.

  The RE content is 1.7% by mass or more and 2.3% by mass or less. By making the RE content 1.7% by mass or more, a sufficient amount of the Al—RE compound is formed in the grains or in the grain boundaries. The compound formed in the grain suppresses deformation of the crystal grain, and the compound formed in the grain boundary suppresses deformation of the magnesium alloy in a high temperature environment by suppressing grain boundary sliding. By making RE content 2.3 mass% or less, it is easy to suppress that an Al-RE compound exists excessively and causes defects, such as a hot crack. Further, the effect of improving the residual axial force and the high temperature creep resistance due to the addition of RE starts to saturate from about 1.7% by mass. Therefore, by setting the RE content to 2.3% by mass or less, an expensive rare earth The amount of element used can be reduced, and the alloy cost can be reduced. The RE content is more preferably 1.8% by mass to 2.2% by mass, and particularly preferably 1.9% by mass to 2.1% by mass.

[Calcium (Ca)]
Ca improves the heat resistance of the magnesium alloy evaluated by the residual axial force. Ca also contributes to the improvement of high-temperature creep resistance against tension. Furthermore, Ca contributes to improving the prevention of molten metal when producing a magnesium alloy. Magnesium alloy melts are easy to ignite, and generally, a preventive gas is used in the production of the melt. However, the use of the preventive gas increases the production cost of the magnesium alloy and is complicated to handle. By adding a predetermined amount of Ca to the molten metal, the prevention property of the molten metal can be improved, and the use of the prevention gas can be reduced or eliminated. Ca forms an Al—Ca compound and exists in the alloy structure. Formation of this Al—Ca compound suppresses the formation (precipitation) of the Mg—Al compound.

  The content of Ca is 0.7% by mass or more and 1.3% by mass or less. By setting the Ca content to 0.7 mass% or more, it is easy to suppress the formation of the Mg—Al compound by sufficiently forming the Al—Ca compound, and thus it is easy to improve the residual axial force and the high temperature creep resistance. . As the Ca content increases, a sufficient amount of the Al—Ca compound is formed in the grains and at the grain boundaries, and the compound suppresses deformation of the magnesium alloy in a high temperature environment. When the Ca content is 1.3% by mass or less, it is easy to suppress the occurrence of defects such as hot cracking due to excessive presence of the Al—Ca compound, and the castability can be improved. The Ca content is more preferably 0.8% by mass or more and 1.2% by mass or less, and particularly preferably 0.9% by mass or more and 1.1% by mass or less.

[Strontium (Sr)]
Sr improves the high temperature creep resistance of the magnesium alloy and improves the prevention of the molten metal. Sr also contributes to lowering the melting point of the magnesium alloy and improving the castability of the magnesium alloy. Sr forms an Al—Sr compound and exists in the alloy structure. By the formation of the Al—Sr compound, the formation (precipitation) of the Mg—Al compound is suppressed.

  The Sr content is 0.2 mass% or more and 0.5 mass% or less. When the Sr content is 0.2% by mass or more, a sufficient amount of the Al—Sr compound is formed in the grains and at the grain boundaries, and the compound improves the high temperature creep resistance of the magnesium alloy. By making the content of Sr 0.5% by mass or less, it is easy to suppress the seizure of the molten metal to the casting mold. The Sr content is more preferably 0.3% by mass or more and 0.5% by mass or less, and particularly preferably 0.4% by mass or more and 0.5% by mass or less.

[Manganese (Mn)]
Mn improves the high temperature creep resistance of the magnesium alloy. Further, Mn reduces Fe that may be present as an impurity in the magnesium alloy and improves the corrosion resistance of the magnesium alloy. Mn forms a compound containing Al (Al—Mn compound) and suppresses the formation (precipitation) of the Mg—Al compound.

  Examples of the Mn content include 0.2% by mass or more and 0.5% by mass or less. By setting the Mn content to 0.2% by mass or more, a sufficient amount of the Al—Mn compound is formed in the grains or at the grain boundaries, and the compound improves the high temperature creep resistance of the magnesium alloy. In addition, the corrosion resistance of the magnesium alloy can be easily improved by setting the Mn content to 0.2% by mass or more. Moreover, formation of a coarse Al-Mn compound can be suppressed because content of Mn shall be 0.5 mass% or less. The Mn content is more preferably 0.2% by mass or more and 0.4% by mass or less, and particularly preferably 0.25% by mass or more and 0.35% by mass or less.

[Organization]
The magnesium alloy has a structure in which the above-described Al-RE compound, Al-Sr compound, Al-Ca compound, and Al-Mn compound are dispersed in crystal grains or in grain boundaries. This magnesium alloy has a structure with little or substantially no Mg—Al compound (β phase). Assuming that all of RE, Sr, Ca, and Mn with the above contents formed a compound with Al, the total amount of Al consumed by these compounds is about 3.3% by mass. In addition, since the solid solubility limit of Al with respect to Mg at 150 ° C. is about 1.5% by mass, theoretically, Al is not crystallized until the Al content is about 4.8% by mass without crystallizing the β phase. It can be estimated that it can be added.

  The structure in which the Mg—Al compound is small or substantially absent is quantitatively a structure in which the area ratio of the Mg—Al compound in the cross section of the magnesium alloy is 5% or less. The smaller the area ratio, the better the high temperature creep resistance, and the more the defects such as hot cracking can be suppressed. The area ratio is preferably 4% or less, and more preferably 2% or less. The area ratio is most preferably 0%, that is, no Mg—Al compound is present.

  These Al-Sr compounds, Al-Ca compounds, Al-Mn compounds, and Al-RE compounds are typically crystallized products. The melting points of the Al—Sr compound and the Al—Ca compound are 1000 ° C. or higher, and the melting point of the Al—RE compound is 1100 ° C. or higher, which is sufficiently higher than the melting point of the Mg—Al compound (462 ° C.). These high melting point compounds such as Al-Sr compounds, Al-Ca compounds, Al-Mn compounds, and Al-RE compounds are dispersed in the grains and grain boundaries, and low melting point compounds such as Mg-Al compounds. It is considered that, when the temperature is kept low, deformation of crystal grains and slipping of grain boundaries can be suppressed, and creep deformation can be made difficult.

Examples of the Al—Sr compound include Al ₂ Sr, Al ₄ Sr, Mg ₁₃ Al ₃ Sr, Mg ₁₁ Al ₃ Sr, Mg ₉ Al ₃ Sr, and the like. Examples of the Al—Ca compound include Al ₂ Ca, Al ₄ Ca, (MgAl) ₂ Ca, and the like. Examples of the Al—Mn compound include Al ₂ Mn. Examples of the Al-RE compound include Al ₂ RE, Al ₁₁ RE _{3 and the} like. Examples of the Mg—Al compound include Mg ₁₇ Al ₁₂ . The composition of these compounds can be confirmed by performing component analysis by, for example, energy dispersive X-ray analysis (EDX) or Auger electron spectroscopy (AES).

The area ratio can be measured as follows. Using the micrograph of the cross section of the magnesium alloy, the Mg—Al compound (mainly Mg ₁₇ Al ₁₂ ) present in the observation visual field Sf (160 μm × 120 μm) is extracted to determine its area, and the total area Sm is further determined. . Then, (Sm / Sf) × 100% is obtained as the area ratio of the Mg—Al compound in the cross section, and the average of the area ratios in the 10 observation fields is defined as the area ratio (%). The cross section can be collected using a commercially available cross section polisher (CP) processing apparatus. The cross-sectional area of the Mg—Al compound can be easily measured by using a binarized image obtained by binarizing a micrograph (SEM image) with an image processing apparatus. The binarization treatment can be performed by distinguishing the Mg—Al compound from the parent phase and other compounds based on the color tone. At this time, the kind of the parent phase and each compound can be confirmed by performing point analysis by EDX.

[Usage]
The magnesium alloy which concerns on embodiment can be utilized suitably for the raw material of various cast members. Applications include, for example, transportation equipment such as automobiles and airplanes, and various electronic and electrical equipment (personal computers (PCs), tablet PCs, mobile phones such as smartphones and folding mobile phones, digital cameras, etc.) Examples include exterior members such as bodies and covers, reinforcing members, and skeleton members.

<Effect>
According to the magnesium alloy according to the embodiment, the following effects can be obtained.
[1] Demonstrates excellent deformation resistance against compressive stress and tensile stress in a high temperature environment. In the magnesium alloy according to the embodiment, Al—Mg compound (β phase) that degrades heat resistance is very little crystallized, and Al—RE, Al—Ca, and Al that are high melting point compounds in grain boundaries and grains. This is because -Sr and the like have a crystallized structure and thus have high heat resistance. Therefore, it can utilize suitably for the raw material of the various cast members of a magnesium alloy.
[2] Excellent flame retardancy. Therefore, since the ignition of the molten metal can be suppressed even if it is melted in the atmosphere, a flameproof gas can be made unnecessary and the manufacturing workability of various cast members of magnesium alloy can be improved.
[3] Seizure hardly occurs on the casting mold. Therefore, manufacturing workability of various cast members of magnesium alloy can be improved.
[4] Defects such as hot cracking are difficult to occur. Therefore, it can utilize suitably for the raw material of the various cast members of the magnesium alloy which has the outstanding external appearance.
[5] Excellent recyclability. The magnesium alloy according to the present embodiment does not require a trace additive element such as Be (beryllium) that easily disappears from the magnesium alloy at the time of remelting in obtaining the above characteristics [1] to [4]. Therefore, when recycling the cast member composed of the magnesium alloy of the present embodiment, it is possible to produce a molten metal as a raw material for a new cast member simply by remelting the cast member.

<Test Example 1>
A die-cast material was prepared using a magnesium alloy, and the heat resistance of the die-cast material was evaluated. The production conditions of the magnesium alloy of the present invention are not limited to the following production conditions of the die-cast material.

  A magnesium alloy melt was prepared. First, 50 kg of a mass of 99.9% by mass of magnesium was prepared and melted at 690 ° C. using a melting furnace in an Ar atmosphere to prepare a pure magnesium melt. Subsequently, a lump of the following additive elements 1 to 5 was added to a completely melted pure magnesium melt to prepare a magnesium alloy melt having the composition shown in Table 1. The addition and dissolution of the additive element was performed by stirring for 10 minutes with a rod-shaped jig while maintaining the hot water temperature at 690 ° C.

1. 1. Pure aluminum mass with a purity of 99.9% by mass 2. Misch metal mass with a purity of 99% by mass 3. Ca mass with a purity of 99.5% by mass 4. Sr mass with a purity of 99% by mass Aluminum master alloy (Al-10 mass% Mn)
The elements contained in the misch metal and the contents thereof are 28 mass% for La, 51 mass% for Ce, 16 mass% for Nd, and 5 mass% for Pr.

  A die-cast material was produced using the magnesium alloy melt of each produced sample. A cold chamber die-casting machine (manufactured by Ube Industries, Ltd., model number UB530iS2) was used for producing the die-cast material. The shape of the die-cast material was an annular plate material having an average thickness of 4 mm. This die-cast material simulates an annular flange used when a member made of a magnesium alloy is fixed to another member. The melt temperature during casting was set at 690 ° C., the injection speed was set at 2.5 m / second, and the casting pressure was set at 60 MPa. The cooling rate during the casting process was set to 50 ° C./second or more.

[Section observation]
The area ratio of the Mg—Al compound (mainly Mg ₁₇ Al ₁₂ ) in the cross section of the die-cast material of each sample prepared was determined. The section was collected using a commercially available cross section polisher (CP) processing apparatus. SEM was used for observation of the cross section. The area ratio of the Mg—Al compound was determined as follows. Using the SEM photograph, the Mg—Al compound (mainly Mg ₁₇ Al ₁₂ ) present in the observation visual field Sf (160 μm × 120 μm) is extracted, and the total cross-sectional area Sm is obtained. Then, (Sm / Sf) × 100% is defined as the area ratio of the Mg—Al compound in the cross section. The number of observation visual fields was 10, and the average of the area ratios in the 10 observation visual fields was defined as the area ratio (%) of the Mg—Al compound in each sample. The results are shown in Table 1. The cross-sectional area of the Mg—Al compound can be easily measured by using a binarized image obtained by binarizing a micrograph (SEM image) with an image processing apparatus.

  As an example, sample no. A micrograph of 1-4 is shown in FIG. In FIG. 1, the dark gray portion is the parent phase of the magnesium alloy, the white portion is the Al-RE compound, and the light gray portion is the Al-Ca compound or Al-Sr compound. As shown in FIG. 1, sample No. 1 containing Al, Sr, Ca, Mn in a specific range. In 1-4, it can be seen that the Al-RE compound, the Al-Sr compound, and the Al-Ca compound are present dispersed in the grains and grain boundaries. Sample No. In 1-4, the Mg—Al compound cannot be confirmed and is substantially absent.

[Evaluation of heat resistance]
About the produced die-cast material of each sample, heat resistance was evaluated as follows. Here, bolt holes are provided at appropriate positions on the block member made of aluminum, and the mounting surface provided with the bolt holes in the block member and the clamping seat surface of the die casting material of each sample are combined, and both bolt holes are made of iron. A test member in which the die-cast material of each sample and the block material were fastened with this bolt was prepared. After holding this test member at 150 ° C. for 170 hours, the fastening force (residual axial force) of the bolt was examined. The residual axial force is a strain amount S ₀ (here, the strain amount when tightened with an initial tightening axial force of 9 N) immediately after fastening and before heating to 150 ° C. by placing a commercially available strain gauge on the bolt, The strain St after giving a thermal history of 150 ° C. × 170 hours was examined, and [(St−S ₀ ) / S ₀ ] × 100 (%) is shown in Table 1 as the residual axial force (%). Further, FIG. 2 shows a graph of residual axial force in which the horizontal axis indicates the Al content and the vertical axis indicates the residual axial force.

  As shown in Table 1 and FIG. 2, the residual axial forces of Samples 1-3, 1-4, and 1-5 were significantly higher than those of the other samples. In particular, referring to FIG. 2, it was found that there is a peak of residual axial force in the portions of samples 1-3, 1-4, and 1-5. In Samples 1-3, 1-4, and 1-5, Al is 4.5% by mass or more and 5.5% by mass or less, the rare earth element is 1.7% by mass or more and 2.3% by mass or less, and Ca is 0.7% by mass. Magnesium containing not less than 1.3% by mass and not more than 1.3% by mass, not less than 0.2% by mass and not more than 0.5% by mass of Sr, not less than 0.2% by mass and not more than 0.5% by mass of Mn, with the balance being Mg and inevitable impurities It is an alloy. Thus, it has been clarified that the heat resistance of the magnesium alloy die-cast material can be improved by adding a predetermined amount of Al and additive elements to the magnesium alloy.

Moreover, as shown in Table 1, the area ratio of Mg ₁₇ Al _{12 in} Samples 1-1 to 1-5 is 5% or less, whereas the area ratio of Samples 1-6 to 1-8 is 5%. More than%. The reason why the heat resistance of Samples 1-6 to 1-8 is low is presumed to be because there is a large amount of Mg ₁₇ Al ₁₂ which is a low melting point compound in the magnesium alloy. On the other hand, the heat resistance of Samples 1-1 and 1-2 is low because the amount of Al added is small, so the amount of Mg ₁₇ Al ₁₂ that decreases heat resistance is small, but the heat resistance is improved. This is presumably because the amount of deposited Al—Sr compound, Al—Ca compound, and Al—RE compound is small.

<Test Example 2>
In Test Example 2, Samples 2-1 to 2-8 in which the RE content was changed were produced, and the residual axial force of each sample was measured. The sample manufacturing method, shape, and residual axial force measurement method are the same as those in the first embodiment. Table 2 shows the compositions and residual axial forces of Samples 2-1 to 2-8. Further, FIG. 3 shows a graph of residual axial force in which the horizontal axis represents the RE content and the vertical axis represents the residual axial force.

  As shown in Table 2 and FIG. 3, as the RE content increases, the effect of improving the residual axial force increases, and the RE content is 1.7 mass% (Sample 2-2). The effect starts to saturate before and after. Since the Al contents of Samples 2-1 to 2-8 are all around 5% by mass, it becomes clear that the effect of improving the value of the residual axial force is not determined only by the Al content. It was. The effect of adding RE is that the content of RE starts to saturate from around 1.7% by mass, so the content of RE is 1.7% by mass (sample 2-4) or more and 2.3. It has also been clarified that the content is preferably not more than mass% (Sample 2-6).

<Test Example 3>
In Test Example 3, Samples 3-1 to 3-9 having different Ca contents were produced, and the residual axial force of each sample was measured. The sample manufacturing method, shape, and residual axial force measurement method are the same as those in the first embodiment. Table 3 shows the compositions and residual axial forces of Samples 3-1 to 3-9. Further, FIG. 4 shows a graph of residual axial force in which the horizontal axis indicates the Ca content and the vertical axis indicates the residual axial force.

  As shown in Table 3 and FIG. 4, as the Ca content increases, the effect of improving the value of the residual axial force increases, and the Ca content is 0.7 mass% (Sample 3-4). The effect starts to saturate before and after. Since the Al contents of Samples 3-1 to 3-9 are all around 5% by mass, it becomes clear that the effect of improving the value of the residual axial force is not determined only by the Al content. It was. Moreover, since the Ca content begins to saturate from around 0.7 mass%, the Ca content is 0.7 mass% (sample 3-4) or more, 1.3 It has also been clarified that the content is preferably not more than mass% (Sample 3-6).

  In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to a claim are included.

Claims (3)

Al is 4.5 mass% or more and 5.5 mass% or less,
1.7% to 2.3% by mass of rare earth elements,
Ca is 0.7 mass% or more and 1.3 mass% or less,
Sr is 0.2% by mass or more and 0.5% by mass or less,
Containing 0.2% by mass or more and 0.5% by mass or less of Mn,
Magnesium alloy with the balance being Mg and inevitable impurities.   The magnesium alloy according to claim 1, wherein the area ratio of the compound containing Mg and Al in the cross section is 5% or less.   The magnesium alloy according to claim 1 or 2, wherein the Al content is 4.8 mass% or more and 5.3 mass% or less.